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Sea sickness

作者:繁蓟    发布时间:2019-03-07 09:13:01    

By Rob Edwards IS POLLUTION leaving porpoises vulnerable to killer diseases? It seems so, now that researchers in London have found the strongest evidence so far linking the contamination of harbour porpoises by polychlorinated biphenyls (PCBs) to deaths from infectious disease. PCBs have long been suspected of damaging the immune systems of whales and dolphins (New Scientist, 1 July 1995, p 12). And sightings of harbour porpoises in the English Channel and southern North Sea suggest that their numbers have been declining since the 1970s. Now Peter Bennett and Paul Jepson of the Institute of Zoology in London have evidence suggesting that PCBs may indeed have had a hand in the porpoises’ decline. With the help of the Centre for Environment, Fisheries and Aquaculture Science at Burnham-on-Crouch in Essex, Bennett and Jepson have been conducting postmortems on harbour porpoises (Phocoena phocoena) stranded around the British coast since 1990. The average level of PCBs in 33 porpoises that had died from infectious diseases was 31.1 milligrams per kilogram of blubber. This compared to 13.6 milligrams per kilogram in 34 otherwise healthy animals that showed signs of having suffocated in fishing nets. “We consider this association may be causal because PCBs have been shown to damage the immune systems of other mammals in the laboratory,” says Bennett. In a second study due to be published next year, Bennett and Jepson have found similar links between fatal infections and levels of mercury in the livers of harbour porpoises. The average concentration of mercury in 37 porpoises killed by disease was 20 milligrams per kilogram, compared to 12.3 milligrams per kilogram in 49 animals that had suffocated in fishing nets. The researchers are investigating the possibility that mercury and PCBs act synergistically, causing additional damage in animals contaminated with both pollutants. PCBs are persistent synthetic compounds previously used as insulators in electrical equipment and in the production of pesticides, lubricants and plastics. Although new uses are now banned in most countries, two-thirds of the 1.5 million tonnes manufactured in Europe and the US prior to 1985 is still inside equipment. Nations surrounding the North Sea have failed to fulfil a commitment they made at a conference of ministers in 1990 to destroy PCBs in use by the end of 1999. Some of the mercury contaminating porpoises may be natural, originating in marine volcanoes, but much of it is thought to be industrial pollution. “We have long believed that pollution was making our marine mammals sick and now we have incontrovertible evidence that this is happening,

 

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